The present invention relates generally to refrigeration systems and more particularly to refrigeration systems incorporating means to prevent overheating of the compressor by selectively injecting liquid refrigerant into the suction manifold.
In response to recent concerns over depletion of the ozone layer due to release of various types of refrigerants such as R12, the government has imposed increasingly stricter limitations on the use of these refrigerants. These limitations will require refrigeration systems of the future to utilize substitute refrigerants. Presently, the available substitutes for commonly used refrigerants such as R-12 and R-502 are not well suited for low temperature applications because they result in high discharge temperatures which may damage or shorten the life expectancy of the compressor particularly under high load situations and high compression ratios.
Liquid injection systems have long been used in refrigeration systems in an effort to limit or control excessive discharge gas temperatures which cause overheating of the compressor and may result in breakdown of the compressor lubricant. Typically, these prior systems utilized capillary tubes or thermal expansion valves to control the fluid injection. However, such systems have been very inefficient and the capillary tubes and thermal expansion valves were prone to leaking during periods when such injection cooling was not needed. This leakage could result in flooding of the compressor. Additionally, when the compressor was shut down, the high pressure liquid could migrate from the receiver to the low pressure suction side through these capillary tubes or expansion valves thereby resulting in slugging of the compressor upon startup. Also, the thermal sensors utilized by these prior systems were typically located in the discharge line between the compressor and condenser. This positioning of the sensor often resulted in inadequate cooling as the sensed temperature could vary greatly from the actual temperature of the discharge gas exiting the compression chamber due to a variety of factors such as the ambient temperature around the discharge line and the mass flow rate of discharge gas. Thus overheating of the compressor could occur due to an erroneous sensed temperature of the discharge gas.
The present invention, however, overcomes these problems by providing a liquid injection system which utilizes a temperature sensor positioned within the discharge chamber of the compressor in close proximity to and in direct contact with the compressed gas exiting the compression chamber. Thus a more accurate indication of the compressor heating is achieved which is not subject to error due to external variables. Further, the present invention employs in a presently preferred embodiment a positive acting solenoid actuated on/off valve coupled with a preselected orifice which prevents leakage of high pressure liquid during periods when cooling is not required. Additionally, the orifice is sized for a maximum flow rate such that it will be able to accommodate the cooling requirements while still avoiding flooding of the compressor. The term "liquid injection" is used herein to denote that it is liquid refrigerant which is taken from the condenser in such systems but in reality a portion of this liquid will be vaporized as it passes through the capillary tube, expansion valve or other orifice thus providing a two phase (liquid and vapor) fluid which is injected into the compressor. The present invention also injects the fluid (i.e. 2 phase fluid) directly into the suction chamber at a location selected to assure even flow of the injected fluid to each compression chamber so as to thereby maximize compressor efficiency as well as to insure a maximum and even cooling effect.
In another embodiment of the present invention the refrigerant fluid is injected directly into the compression chamber preferably immediately after the suction ports or valve has been closed off thus acting to cool both the compression chamber and suction gas contained therein. While this arrangement offers greater efficiency in operation, it tends to be more costly as additional controls and other hardware are required for its implementation.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.